This invention relates to electric vehicles and to control circuits therefor. It particularly relates to road delivery vehicles.
It would be an advantage to provide higher road speeds than are currently available on electric delivery vehicles, particularly as now there is a tendency, with centralisation of supply, for the individual delivery round to become longer - it may extend up to ten miles or more from the depot. However, this results in a greater energy requirement and there is obviously a finite amount of energy available per trip, or between charges in the case of a battery-operated vehicle. Furthermore, if a driver is given a higher speed capability and he attempts to use it on every possible occcasion there will be frequent stoppings from high speed which is very wasteful of energy and the latter may not suffice to enable the round to be completed. In any case high speeds are not necessary when a vehicle is on a frequent stop-start run and do not materially affect the total delivery round time.
In one prior art arrangement the vehicle battery is in two sections. These sections are initially connected, by means of switches, so that they are in parallel across a series circuit comprising a rheostat controller and the drive motor. When the driver wishes to go faster than can be provided by this circuit arrangement the connections are switched so that the sections are connected in series. The speed is then regulated by means of a further rheostat connected in the series circuit. This arrangement permits the driver to select the higher speed range at any time and is therefore not satisfactory for delivery vehicles. The additional rheostat furthermore wastes energy.
In a further arrangement, which is similar to the previously mentioned one, diodes are connected in place of switches in series with the individual sections of the battery and these diodes become back-biassed when the batteries are switched to a series connection thus preventing short circuits on the batteries. This arrangement offers considerable economies but still allows the driver to select the higher speed range whenever it suits him.
It is an object of this invention to provide an electric battery powered vehicle having an extendable speed range which may be used only on relatively long journeys.
According to the present invention, there is provided an electric battery powered vehicle having both a variable speed controller and a manual range control for changing the speed range capability of the vehicle by at least one step, and further comprising a delay means which temporarily renders the manual range control inoperative when the vehicle starts so as to prevent the upper fraction of the speed range being available to the driver during short journeys such as occur with house to house deliveries. If, for example, it is impossible for the driver to achieve more than half speed for a period of, say, ten seconds, short distance house to house vehicle movements will perforce be made in the low speed mode, without the energy losses consequent upon frequent stopping from high speeds, and yet the higher speed capability will be available for longer distances.
In a preferred embodiment, the driver depresses a footswitch to accelerate the vehicle from rest in a fully controlled manner but during the first ten seconds, say, of travel the top speed is limited to half of the overall maximum speed. At the end of the timed period, a visual indication may be provided to the driver that maximum speed is now available but the vehicle does not accelerate beyond half speed unless the driver operates a control, e.g., a switch or button, for this purpose. When the high speed indication is showing and the driver's control is operated the vehicle accelerates under full control to maximum speed (and full power).
In both modes of operation of the preferred embodiment, the actual power supplied to the traction motor through the controller is under the control of the driver via the footswitch. However, it will be understood that, in the limited or half speed mode, there need not always be a restriction to half power in all cases because the vehicle may need more power to climb a steep gradient at low speed. But when the vehicle is travelling on level road, the half-speed mode will involve a limitation of the power available to that appropriate to maintain that speed.
As a further feature, attempts by the driver to operate the top speed button during the initial timed period may be arranged to cause the timer to reset and the timing period to recommence. This is expected to discourage undesirably early attempts to achieve the top speed mode. The timer may also be arranged to reset as a consequence of slowing down or stopping of the vehicle and this will prevent the driver from using his waiting period or some part of it during some short journeys so that on a later journey he may immediately assume a high speed operation.